Workshop on monoclonal antibodies to human melanoma-associated antigens: findings of the Seattle group

Identification of a novel serum protein secreted by lung carcinoma cells

The murine anti-human lung tumor monoclonal antibody L3 recognizes antigens found both in the medium of cultured carcinoma cells and in normal human serum. Sequential immunoprecipitation experiments indicate that the L3 antigen is also recognized by a previously described monoclonal antibody directed against a melanoma-associated antigen [Natali, P. G., Wilson, B. S., Imai, K., Bigotti, A., & Ferrone, S. (1982) Cancer Res. 42, 583-589]. This antibody precipitated a Mr 76000 glycoprotein from metabolically labeled extracts of the lung carcinoma cell line Calu-1 and a Mr 94 000 glycoprotein from labeled culture medium. Pulse-chase experiments suggested a precursor-product relationship between these molecules. Analysis of glycosidase sensitivities of the two forms indicated that maturation of carbohydrate side chains correlated with the apparent increase in molecular weights. L3 antigenic activity, measured in a competitive radiometric cell binding assay, was purified more than 90-fold from serum-free medium of Calu-1 cells and more than 3000-fold from normal human serum. The major immunoreactive components purified from culture medium and serum were identical with respect to apparent molecular weight, electrophoretic mobility, pI, glycosidase sensitivity, and V8 protease fingerprints. In addition, the sequence of the amino-terminal 16 N-terminal amino acid residues of the major immunoreactive species from both sources was identical. The properties of the L3 antigen did not correspond to those of any known protein, suggesting that this serum protein has not been previously characterized.

A monoclonal antibody against basal cells of human epidermis. Potential use in the diagnosis of cervical neoplasia

A murine monoclonal antibody was generated against human skin cells obtained from psoriatic plaques. The antibody, called VM-2, recognizes an epitope expressed on the basal cell layer of human skin and other epithelia. VM-2 also binds to cultured cells from a variety of human carcinomas including HeLa cervical carcinoma, A-431 vulvar carcinoma, A-549 lung alveolar carcinoma, and SCL-1 skin squamous cell carcinoma cells. In several primary human cell lines, including fibroblasts, endothelial cells, and cells from the hematopoietic lineage, the antigenic site recognized by VM-2 could not be detected. The cellular antigen when immunoprecipitated by VM-2 from both normal and transformed cells appears to be proteins of approximately 100,000 and 120,000 mol weight. In frozen sections from human tumor-containing tissues, VM-2 labels skin, cervical, and lung squamous carcinoma cells, as well as skin basal carcinoma cells. Malignant cells present in exfoliative smears from epidermoid invasive neoplasias of the cervix are also selectively recognized by VM-2 in distinction to normal squamous cervical cells. VM-2 is thus directed against an antigen associated with neoplastic cells when applied in selected sites of exfoliative cytology. This monoclonal antibody represents a new reagent that should prove useful in the diagnosis of cervical neoplasia.

Monoclonal antibodies that prevent adhesion of B 16 melanoma cells and reduce metastases in mice: crossreaction with human tumor cells

Monoclonal antibodies raised against B 16 melanoma cells in syngeneic mice were functionally screened for their ability to inhibit cell adhesion in tissue culture. Three of these antibodies (16/43, 16/77, 16/82), when preinjected into C57BL/6 mice, markedly reduced the number of experimental lung metastases produced by B 16 cells, possibly by interference with their adhesion to the lung endothelia. We now report that these monoclonal antibodies block in vitro attachment of the majority of human melanoma cell lines tested and also of carcinoma, neuroblastoma, and glioblastoma cells from both mice and humans but untransformed cell lines such as 3T3 mouse or MRC-5 human fibroblasts are not affected. The antibodies also react with mouse teratocarcinoma stem cells (F9, PCC4) but not with differentiated teratocarcinoma lines (PYS-2, 944). Furthermore, the antiadhesion activity of the antibodies could be quantitatively absorbed by intact human and mouse tumor cells but not by untransformed cells, suggesting that the corresponding antigens may represent tumor-associated cell surface components. Correspondingly, the antigens were found on simian virus 40-transformed 3T3 mouse fibroblasts and are expressed in a temperature-sensitive fashion in chicken fibroblasts transformed with a temperature-sensitive Rous sarcoma virus. On "immunoblots" of NaDodSO4-containing gels the three selected antibodies (16/43, 16/82, 19/1) were absorbed by antigens with molecular weights of 40,000 and 50,000.